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United States Patent |
5,224,842
|
Dziorny
,   et al.
|
July 6, 1993
|
Air cycle machine with interstage venting
Abstract
An air cycle machine (10) having a plurality of wheels mounted on a common
shaft (20) for rotation therewith about a longitudinal axis (12),
including a compressor rotor (60) and a turbine rotor (50) mounted to a
central portion (20c) of the shaft in back to back relationship, the
turbine rotor (50) being operative to extract energy from a flow of
compressed air for driving the shaft (20), and the compressor rotor (60),
in rotation about the axis. An annular disc-like member (14) is disposed
coaxially about the shaft (20) and extends radially outwardly between the
turbine rotor (50) and the compressor rotor (60). A venting and sealing
assembly (210, 220, 230) is operatively disposed between the shaft (20)
and the annular member (14) intermediate the turbine rotor (50) and the
compressor rotor (60) whereby a limited flow of compressor outlet air and
a limited flow of turbine inlet air are vented to a low pressure region
other than the turbine air flow circuit.
Inventors:
|
Dziorny; Paul J. (132 Strawberry La., Manchester, CT 06040);
McAuliffe; Christopher (18 Kellogg St., Windsor, CT 06095)
|
Appl. No.:
|
819426 |
Filed:
|
January 10, 1992 |
Current U.S. Class: |
417/406 |
Intern'l Class: |
F04B 017/00 |
Field of Search: |
417/406,405
62/401,402
|
References Cited
U.S. Patent Documents
2283176 | May., 1942 | Birmann | 417/406.
|
2864552 | Dec., 1958 | Anderson | 417/406.
|
2973136 | Feb., 1961 | Greenwald | 62/402.
|
3069133 | Dec., 1962 | Swearingen | 417/406.
|
3133425 | May., 1964 | Hanny et al. | 62/402.
|
3428242 | Feb., 1969 | Rannenberg | 415/180.
|
3728857 | Apr., 1973 | Nichols | 62/402.
|
4086760 | May., 1978 | Chute | 417/406.
|
4312191 | Jan., 1982 | Biagini | 62/402.
|
4507939 | Apr., 1985 | Wieland | 62/402.
|
4543038 | Sep., 1985 | Kitaguchi | 417/406.
|
5113670 | May., 1992 | McAuliffe et al. | 417/406.
|
Foreign Patent Documents |
918726 | Oct., 1954 | DE | 417/406.
|
3322436 | Jan., 1985 | DE | 417/406.
|
Primary Examiner: Bertsch; Richard A.
Assistant Examiner: Thorpe; Timothy S.
Attorney, Agent or Firm: Habelt; William W.
Claims
We claim:
1. An air cycle machine for conditioning air for supply to an enclosure,
said air cycle machine comprising:
shaft means supported for rotation about a longitudinally extending axis;
a compressor wheel mounted to said shaft means for rotation therewith for
compressing air delivered thereto;
a turbine wheel mounted to said shaft means for expanding compressed air
from said compressor wheel thereby extracting energy to drive said shaft
means in rotation about the axis, said turbine wheel and said compressor
wheel disposed in back-to-back relationship;
a stationary annular disk-like member disposed coaxially about said shaft
means and extending radially outwardly between said turbine wheel and said
compressor wheel, said annular disk-like member having a radially inward
portion having an inward rim surface circumscribing said shaft means at a
radial spacing therefrom thereby defining an annular space between said
shaft means and said annular disk-like member;
a turbine inlet duct circumscribing said turbine rotor for directing a flow
of relatively cooler relatively high pressure air into said turbine rotor
to be expanded in said turbine;
a compressor outlet duct circumscribing said compressor rotor for
discharging a flow of relatively warmer relatively high pressure air
passing out of said compressor;
means for venting the annular space defined between said shaft means and
said annular disk-like member to a low pressure region; and
means for sealing the annular space defined between said shaft means and
said annular disk-like member from the turbine inlet duct and from the
compressor outlet duct whereby a limited flow of turbine inlet air and a
limited flow of compressor outlet air leaks pass said sealing means into
the annular space defined between said shaft means and said annular
disk-like member and thence through said vent means into the low pressure
region.
2. An air cycle machine as recited in claim 1 wherein said vent means
comprises a plurality of holes extending through said shaft means and
disposed at circumferentially spaced intervals about said shaft means,
each hole providing a flow passageway between the annular space and a low
pressure interior cavity of said shaft means.
3. An air cycle machine as recited in claim 2 wherein said holes are
selectively sized to limit the flow into the low pressure region whereby
the annular volume is maintain at a pressure about equal to the pressure
of the flow of turbine inlet air that leaks pass said sealing means into
the annular space.
Description
TECHNICAL FIELD
The present invention relates generally to air conditioning systems for
cooling and dehumidifying air for supply to an aircraft cabin or like
enclosure and, more particularly, to an air cycle machine having a turbine
rotor and a compressor rotor mounted on a common drive shaft in
back-to-back relationship.
BACKGROUND ART
Conventional aircraft environmental control systems incorporate an air
cycle machine, also referred to as an air cycle cooling machine, for use
in cooling and dehumidifying air for supply to the aircraft cabin for
occupant comfort. Such air cycle machines may comprise two, three or four
wheels disposed at axially spaced intervals along a common shaft, and
defining a compressor rotor, a turbine rotor, and one or two additional
rotors, for example a fan rotor or an additional turbine rotor or an
additional compressor rotor, the turbine or turbines driving both the
compressor and the fan. The wheels are supported for rotation about the
axis of the shaft on one or more bearing assemblies disposed about the
drive shaft. Although the bearing assemblies may be ball bearings or the
like, hydrodynamic film bearings, such as gas film foil bearings, are
often utilized on state-of-the-art air cycle machines.
Each wheel may comprise only a single rotor, such as, for example,
disclosed in commonly assigned U.S. Pat. No. 3,428,242. The three wheel
air cycle machine disclosed therein comprises a fan rotor, a turbine rotor
and a compressor rotor mounted to a common shaft, with the fan rotor being
disposed at one end of the shaft and the turbine and compressor rotors
being disposed at the other end of the shaft. The shaft is supported for
rotation on a ball bearing assembly disposed intermediate the fan and the
turbine and cooled by turbine outlet air. The compressor rotor and the
turbine rotor are disposed in back to back relationship on opposite sides
of a central plate with the turbine inboard of the compressor. The central
plate disposed between the turbine and compressor rotors forms part of the
housing encasing the turbine and compressor rotors and defining separate
inlet and outlet ducts for the turbine rotor and the compressor rotor. In
this arrangement, the central plate is exposed on its outboard side to
relatively warmer air being ducted from the compressor rotor and is
simultaneously exposed on its inboard side to relatively cooler air being
ducted to the turbine rotor.
It is also known in the art for a single wheel to comprise a dual rotor,
that is for a single wheel to provide two back-to-back rotors either
formed integrally as one piece or integrally mounted together. For
example, U.S. Pat. No. 4,312,191, discloses an air cycle machine including
a dual rotor wheel mounted on a bearing assembly disposed about an axially
extending shaft. This dual rotor wheel comprises a turbine disk and a
compressor disk disposed in back-to-back relationship with the compressor
disk integrally secured to the turbine disk. The dual rotor wheel is
disposed within a housing defining the flow ducts to and from the
compressor and turbine rotors and having a central annular plate portion
which separates the turbine inlet flow duct from the compressor outlet
flow duct. The central plate may be an integral part of the housing or
formed by mating two housing segments together to encase the dual rotor
wheel. In either case, the central plate is exposed on one side to
relatively warmer air being ducted from the compressor rotor, while
simultaneously being exposed on its other side to relatively cooler air
being ducted to the turbine rotor.
On aircraft powered by turbine engines, the air to be conditioned in the
air cycle machine is typically compressed air bled from one or more of the
compressor stages of the turbine engine. In conventional systems, this
bleed air is passed through the air cycle machine compressor wherein it is
further compressed, thence passed through a condensing heat exchanger to
cool the compressed air sufficiently to condense moisture therefrom
thereby dehumidifying the air before expanding the dehumidified compressed
air in the turbine of the air cycle machine to both extract energy from
the compressed air so as to drive the shaft and also to cool the expanded
turbine exhaust air before it is supplied to the cabin as conditioned
cooling air.
The compressed bleed air being supplied to the compressor of the air cycle
machine is typically supplied at a temperature of about 105.degree. C. to
about 120.degree. C., but raised in temperature during the compression
process to a temperature typically in the range about 150.degree. C. to
about 175.degree. C. The temperature of the compressed air is thereafter
reduced prior to being delivered to the turbine for expansion therein to a
temperature typically in the range of about 40.degree. C. to about
50.degree. C. to dehumidify the air, and thence further cooled in the
expansion process to a temperature typically less than 5 degrees Celsius
above the freezing point of 0.degree. C. Consequently, the temperature
difference between the compressor outlet air and the turbine inlet air
flowing on opposite sides of the central plate may range from 80 to 125
degrees Celsius.
In air cycle machines having separate compressor and turbine wheels
disposed on a common rotor shaft in back-to-back relationship on opposite
sides of a stationary central plate separating the compressor and turbine
flow circuits, leakage of higher pressure air from the compressor outlet
circuit into the lower pressure air flowing through the turbine inlet
circuit can occur. Such leakage has an undesireable impact on air cycle
machine performance as the consequent transfer of heat from the relatively
warmer air flow leaking from the higher pressure compressor outlet air
flow into and mixing with the relatively cooler air flow in the lower
pressure turbine inlet circuit reduces the effective cooling efficiency of
the expansion process. Since cooling the air flow is the primary function
of the expansion turbine, this undesireable leakage of heat into the
cooler turbine inlet air flow detracts from the attractiveness of such a
back-to-back arrangement, which is generally otherwise desireable as a
means of minimizing the overall length, and therefore weight, of the air
cycle machine.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide an air cycle machine
having back-to-back compressor and turbine rotors wherein a combined
sealing and venting arrangement is provided for limiting the leakage of
the relatively warmer compressor outlet air flow into the relatively
cooler turbine inlet air flow.
It is an additional object of a particular embodiment of the present
invention to provide an air cycle machine having back-to-back compressor
and turbine rotors incorporating a sealing arrangement comprising a pair
of spaced knife edge seals extending outwardly from the rotor shaft
intermediate the turbine and compressor rotors and contacting in sealing
relationship a seal land mounted to the inboard end of a stationary
central member disposed between the turbine and compressor rotors.
It is a further object of a specific embodiment of the present invention to
provide an air cycle machine incorporating a plurality of vent holes
disposed intermediate the spaced knife edge seals for venting a limited
flow of compressor outlet air and/or turbine inlet air flow leaking past
the seals to a low pressure region.
The air cycle machine of the present invention comprises a turbine rotor
and a compressor rotor disposed in back-to-back relationship on a common
shaft means for rotation therewith about a longitudinal axis and encased
in a housing defining a turbine flow circuit and a compressor flow
circuit, a stationary central member, such as an annular disk-like member,
disposed coaxially about the shaft means and extending between the turbine
and compressor rotors, and means for limiting the leakage of relatively
warmer, higher pressure compressor outlet air into the relatively cooler,
lower pressure turbine inlet air flow comprising sealing and venting means
operatively disposed about the shaft means intermediate the turbine and
compressors and in sealing relationship between the shaft means and the
stationary central member.
In a particularly advantageous embodiment of the present invention, the
sealing and venting arrangement comprises two sets of knife edge elements
extending outwardly from the shaft means in spaced relationship
intermediate the turbine rotor and the compressor rotor, seal land means
mounted to the radially inboard end of the annular disk-like central
member in sealing relationship with each set of knife edge elements, and
vent hole means disposed between the spaced sets of knife edge elements.
The vent hole means may comprise a plurality holes provided in the shaft
means opening to a low pressure interior region thereof or a plurality of
holes provided in the stationary central member opening therethrough to an
external low pressure region. In either case, a small amount of compressor
outlet air flow is deliberately passed through a first volume formed
between the backside of the compressor rotor and an inboard root portion
of the central member to leak past one of the knife edge seals and through
the vent hole means, while at the same time a small amount of turbine
inlet air flow is deliberately passed through a second volume formed
between the backside of the turbine rotor and the root portion of the
central member to leak past the other of the knife edge seals and through
the vent hole means.
The compressor air flow leaking past the knife edge seal will be desireably
vented through the vent hole means to a low pressure region rather than
passing into the turbine inlet circuit, thereby avoiding mixing of the
warmer compressor outlet air flow with the cooler air flow passing into
the turbine. Additionally, as the region between the spaced seals and
upstream of the vent hole means will be maintained at a pressure between
that of the compressor outlet air flow and that of the low pressure
region, the leakage of turbine inlet air flow through the venting circuit
will be desireably limited.
BRIEF DESCRIPTION OF DRAWING
These and other objects, features and advantages of the present invention
will become more apparent in light of the detailed description of the
embodiment thereof illustrated in the accompanying drawing, wherein:
FIG. 1 is a side elevational view, partly in section, of a four wheel air
cycle machine incorporating the present invention;
FIG. 2 is an enlarged side elevational view, partly in section, of the
region 2--2 of the embodiment of the present invention illustrated in FIG.
1;
FIG. 3 is a further enlarged, sectioned, side elevational view of region
3--3 of the embodiment of the present invention illustrated in FIG. 2; and
FIG. 4 is a cross-sectional view taken along 4--4 of FIG. 3.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIG. 1, there is depicted therein an air cycle machine 10
having four distinct wheels coaxially disposed along a common shaft means
20 for rotation about a common longitudinal axis 12. A first wheel 30 is
mounted to a first end portion 20a of the shaft means 20 for rotation
therewith, a second wheel 40 is mounted to a second end portion 20b of the
shaft means 20 for rotation therewith, a third wheel 50 is mounted to a
central portion 20c of the shaft means 20 in spaced relationship from the
first wheel 30 and the second wheel 40 for rotation therewith, and a
fourth wheel 60 is also mounted to the central portion 20c of the shaft
means 20 for rotation therewith in back-to-back relationship with the
third wheel 50 and between the second wheel 40 and the third wheel 50. The
shaft means 20 is supported for rotation about the longitudinal axis 12 on
a pair of spaced bearing means 70 and 80 supported in a housing 100 which
serves not only to support the bearing means, but also to provide
appropriate inlet ducts and outlet ducts for the supply of working fluid
to and the discharge of working fluid from each of the four wheels.
In the air cycle machine 10 embodying the present invention, one of the two
wheels mounted to the central portion 20c of the shaft means 20, that is
either the third wheel 50 or the fourth wheel 60, comprises a compressor
rotor operative to compress a flow of gaseous working fluid and the other
of the central wheels comprises a turbine rotor operative to expand the
gaseous working fluid compressed via the compressor rotor thereby
extracting energy therefrom so as to drive the shaft means 20 in rotation
about the axis 12 and thereby power the compressor rotor. The two outer
wheels, that is the first wheel 30 and the second wheel 40, may each
comprise a fan rotor, or one may comprise an additional turbine rotor and
the other a fan rotor, or one may comprise an additional turbine rotor and
the other an additional compressor rotor, as desired. In fact, the wheels
of an air cycle machine embodying the present invention may comprise any
rotor combination having at least one turbine rotor and at least one
compressor rotor wherein the turbine rotor and the compressor rotor are
mounted on a common shaft in back-to-back relationship, with the turbine
rotor extracting sufficient energy from the gaseous working fluid expanded
therein to drive the shaft means 20, and the compressor rotor, and any
other rotor or rotors, as the case may be, mounted on the common shaft
means 20 in rotation therewith about the axis 12.
Each of the shaft members 20a, 20b and 20c comprise an annular sleeve
defining an open ended hollow central cavity. The end shaft members 20a
and 20b are supported for rotation about the longitudinal axis 12 on
bearing means 70 and 80, respectively. Each of the four wheels 30, 40, 50
and 60 is a rotor comprising a hub portion and a plurality of rotor blades
extending outwardly from the hub portion. The hub portion of each rotor
has a central opening extending axially therethrough to accommodate an
elongated tie rod 16 extending along the longitudinal axis 12 through the
central axial openings in the four wheels and through the hollow cavities
of the shaft members. The tie rod 16 is bolted up at its ends to the outer
wheels 30, 40 to axially clamp the four wheels and the shaft members
together with sufficient axial clamping load that all four wheels and all
shaft members rotate together as one integral wheel and shaft assembly.
The first end wheel 30 is mounted to the outboard end of the first end
shaft member 20a and the second end wheel 40 is mounted to the outboard
end of the second end shaft member 20b. The central wheel 50 is mounted to
the inboard end of the first end shaft member 20a and the central wheel 60
is mounted to the second end shaft member 20b. The two central wheels 50
and 60 are additionally mounted to the central shaft member 20c for
rotation therewith and disposed in back to back relationship on opposite
sides of an annular disc-like member 14 having a central opening
circumscribing the central shaft member 20c and extending radially
outwardly therefrom. Each of the wheels 30, 40, 50 and 60 is mounted to
its respective end shaft member 20a, 20b by an interference fit between a
piloting rim 32, 42, 52, 62, respectively, extending axially outwardly
from the wheel hub, and the inner wall of the shaft member bounding the
central cavity thereof into which cavity the rim is precisely piloted,
thereby ensuring that the wheels and the shaft members rotate together
about the axis 12.
Alternate methods of mounting the wheels to the shaft members be may used
in constructing the air cycle machine 10. For example, as best seen in
FIG. 2, the third wheel 50 is not mounted to the central shaft member 20c
by means of a piloting rim, but rather is mounted to the central shaft
member 20c through a pilot bushing 18 coaxially disposed about the axis
12. The hub of the third wheel 50 has a central piloting socket 54 sized
to receive and retain by interference fit one end of the pilot bushing 18.
The other end of the pilot bushing 18 is received into one end of the
central cavity of the central shaft member 20c and retained therein by
interference fit with the inner wall of the central shaft member 20c. The
fourth wheel 60 is mounted to the central shaft member 20c through a
piloting rim 64 which is received into the other end of the central cavity
of the central shaft member 20c and retained therein by interference fit
with the inner wall thereof. The four wheels and the three shaft members
to which they are so mounted are axially loaded together by the tie rod 16
extending coaxially therethrough, thereby ensuring that the four wheels
and the three shaft members rotate together about the longitudinal axis 12
as a single assembly. The pilot bushing 18 also serves to center the
entire wheel and shaft assembly coaxially about the tie rod 16.
The wheel and shaft assembly is disposed within a housing 100 which
provides individual inlet and outlet ducts for each of the rotors and also
provides support for the bearing means 70 and 80. The housing 100 may
advantageously be comprised of two or more sections to facilitate
assembly. The bearing means 70 and 80 radially supporting the shaft and
wheel assembly for rotation about the longitudinal axis 12 may comprise
hydrodynamic journal bearings, such as for example gas film foil journal
bearings of the type disclosed in commonly assigned U.S. Pat. Nos.
4,133,585; 4,247,155; and/or 4,295,689. The hydrodynamic journal bearing
70 is disposed about the first end shaft member 20a between the first
wheel 30 and the third wheel 50, and the hydrodynamic journal bearing 80
is disposed about the second end shaft member 20b between the second wheel
40 and the fourth wheel 60. Each of the hydrodynamic bearings 70 and 80
comprises an inner race mounted to its respective shaft member, an outer
race disposed coaxially about the inner race in radially spaced
relationship therefrom and supported in the housing 100 to restrict axial
or rotational displacement of the outer race, and a foil pack disposed in
an annular space formed between the radially spaced inner and outer races
through which pressurized air is passed to provide the appropriate
hydrodynamic forces necessary for the journal bearings 70 and 80 to
support the shaft and wheel assembly for rotation about longitudinal axis
12.
Additionally, a hydrodynamic thrust bearing 26 is provided for axially
supporting the shaft and wheel assembly of the air cycle machine 10. The
hydrodynamic thrust bearing may comprise a gas film foil thrust bearing,
such as for example of the type disclosed in commonly assigned U.S. Pat.
Nos. 4,082,325; 4,116,503; 4,247,155 and/or 4,462,700. The bearing 26
includes an outboard bearing member 26a and an inboard bearing member 26b
operatively disposed on opposite sides of a thrust disc 90 extending
outwardly from the first end shaft member 20a intermediate an end wall 116
of the central housing section 110 and a bearing plate 118 disposed
between the central housing section 110 and the first end section 120
inboard of the outboard first wheel 30.
In the air cycle machine 10 as illustrated in the drawing, the central
third wheel 50 comprises a first stage turbine rotor, the central fourth
wheel 60 comprises a compressor rotor, the outboard first wheel 30
comprises a second stage turbine rotor, and the outboard second wheel 40
comprises a fan rotor. The first and second stage turbine rotors 30 and 50
serve not only to expand and cool the air being conditioned, but also
extract energy from the air being expanded for rotating the entire wheel
and shaft assembly so to drive the fan rotor 40 and the compressor rotor
60. This embodiment of the air cycle machine 10 is particularly suited for
use in a condensing cycle air conditioning and temperature control system
for cooling and dehumidifying air for supply to an enclosure for occupant
comfort, such as the condensing cycle environmental control system for
supplying cooled and dehumidified air to the cabin of an aircraft as
disclosed in commonly assigned, U.S. Pat. No. 5,086,022, co-pending
application serial no. filed Aug. 17, 1990, which is hereby incorporated
by reference.
In the illustrated embodiment of the air cycle machine 10, the housing 100
is comprised of three sections: a central section 110 surrounding the
turbine rotor 50 and providing a first stage turbine inlet duct 152
circumscribing the turbine rotor 50 radially outwardly thereof for
supplying air to the turbine rotor 50 to be expanded therein and providing
a first stage turbine outlet duct 154 axially adjacent the outlet of the
turbine rotor 50 for discharging the exhaust air expanded in the turbine
rotor 50, a first end section 120 surrounding the turbine rotor 30 and
providing a second stage turbine inlet duct 132 for supplying air to the
turbine rotor 30 to be expanded therein and an axially directed second
stage turbine outlet duct 134 for discharging the exhaust air expanded in
the turbine rotor 30, and a second end section 130 surrounding both the
compressor rotor 60 and the fan rotor 40 and providing an inlet duct 162
axially adjacent the inlet to the compressor rotor 60 for supplying air to
the compressor rotor 60 to be compressed therein, an outlet duct 164
circumscribing the compressor rotor 60 radially outwardly thereof for
discharging air compressed via the compressor rotor 60, an inlet duct 142
for directing ram cooling air to the fan rotor 40 and an axially directed
outlet duct 144 for discharging ram cooling air having passed through the
fan rotor 40. The central housing section 110 is mounted at one of its
ends to the first end housing section 120 by a plurality of
circumferentially spaced bolts 102 attaching a flange 112 of the central
section 110 to a flange 122 of the end section 120, and at its other end
to the second end housing section 130 by a plurality of circumferentially
spaced bolts 104 passing through the annular disc-like member 14 to attach
flange 114 of the central section 110 to flange 124 of the end section
130.
To cool and pressurize the thrust bearing 26 and the journal bearings 70
and 80 during operation, relatively cool, pressurized air from the second
stage turbine inlet duct 132 is passed through a flow tube 28 into an
annular chamber 34 located between the bearing plate 118 and the end wall
116. A first portion of this cool pressurized air flows therefrom through
the outboard thrust bearing member 26a to pressurize and cool this bearing
member and thence through openings 36 in the outboard end portion of the
first end shaft member 20a into the hollow interior cavity 21 thereof. A
second portion of this cool pressurized air flows from the chamber 34
through the inboard thrust bearing member 26b and thence through the first
journal bearing 70 to cool and pressurize both of these hydrodynamic
bearings. After traversing the first journal bearing 70, this second
portion of the cool pressurized air passes through openings 38 in the
inboard end portion of the first end shaft member 20a into the hollow
interior cavity 21 thereof to remix with the first passes through the
hollow interior of the shaft and wheel assembly to pass through openings
44 in the inboard end portion of the second end shaft member 20b to enter
a chamber 46 from which this cool pressurized air passes through the
second journal bearing 80, thereby cooling and pressuring the second
hydrodynamic journal bearing 80, before exiting past a seal 48, such as a
labyrinth seal, into the duct 142. Additional seals 58 and 68, also
depicted as labyrinth seals, are provided to prevent the bearing cooling
and pressurizing air from escaping the bearing flow circuit. Seal 58,
which is disposed between the inboard end portion of the first end shaft
member 20a and the inboard end of the first journal bearing 70, allows a
limited flow of higher pressure, cool air from the first stage turbine
outlet duct 154 to leak into the bearing flow circuit thus sealing the
first journal bearing 70, and seal 68, which is disposed between the
inboard end portion of the second end shaft member 20b and the surrounding
housing, allows a limited flow of higher pressure, relatively cool air to
leak from the compressor inlet duct 162 into the chamber 46 thereby
sealing the second journal bearing 80.
Referring now particularly to FIGS. 2 and 3, the central member comprises a
stationary annular disc-like member 14 disposed coaxially about the
central shaft member 20c and extending therefrom radially outwardly such
that a radially inward root portion 14a thereof is disposed between the
backside of the compressor rotor 60 and the backside of the turbine rotor
50 and a radially outer portion 14b of the annular disk-like member is
disposed between the central housing section 110 and the second housing
section 130 to separate the air flow circuit associated with the
compressor rotor 60 from the air flow circuit associated with the turbine
rotor 50 over at least a substantial part of their extent, preferably so
as to extend between and separate between the inlet duct 152 of the
turbine flow circuit and the outlet duct 164 of the compressor flow
circuit. The annular disk-like member 14 is disposed about the cylindrical
central shaft sleeve 14c with its radially inward rim surface 14c spaced
radially outwardly therefrom so as to circumscribe the shaft sleeve 20c at
a radial spacing therefrom thereby defining an annular space therebetween.
Advantageously, the radially inward root portion 14aof the annular
disk-like member 14 separating the back-to-back rotors 50 and 60 is
disposed therebetween in spaced relationship with both the turbine rotor
50 and the compressor rotor 60 so as to provide a first volume 61 between
member 14 and the backside of the compressor rotor 60 which is open to the
compressor outlet duct 164 through a relatively small annular passage 63
and to provide an second volume 51 between member 14 and the backside of
the turbine rotor 50 which is open to the turbine inlet duct 152 through a
relatively small annular passage 53.
In accordance with the present invention, sealing and venting means 200 is
operatively disposed about the central shaft member 20c at a location
intermediate the turbine rotor 50 and the compressor rotor 60 for
establishing a sealing relationship between the outer surface of the
central shaft 20c of the shaft means 20 and the radially inward annular
rim surface 14c of the annular disc-like member 14 disposed about the
central shaft member 20c between the turbine rotor 50 and the compressor
rotor 60. The sealing and venting means 200 comprises vent means 210 and a
pair of seal means 220 and 230 disposed in axially spaced relationship
along the central shaft member 20c so as to define an annular volume 205
between the annular disk-like member 14 and the central shaft member 20c,
which is bounded radially outwardly by the inward annular rim surface 14c
of the annular disc-like member 14 and radially inwardly by the outer
surface of the cylindrical central shaft sleeve 20c, and axially by the
first seal means 220 at one end and the second seal means 230 at the other
end. Vent means 210 opens to the annular volume 205 defined between the
axially spaced seal means 220 and 230 for venting air flow leaking into
the annular volume 205 to a low pressure region as will be discussed in
more detail hereinafter. The first seal means 220 functions to limit the
flow of turbine inlet air leaking into the annular volume 205 and the
second seal means 230 functions to limit the flow of compressor outlet air
leaking into the annular volume 205. The annular volume 205 is vented via
vent means 210 to a region maintained at a pressure which is lower than
both the pressure of the turbine inlet air in the annular volume 51 on the
backside of the turbine rotor 50, termed the turbine backside pressure,
and the pressure of the compressor outlet air in the annular volume 61 on
the backside of the compressor rotor 60, termed the compressor backside
pressure. Therefore, the pressure within the annular volume 205 is
maintained at a pressure between the low pressure of the region to which
the vent means 210 opens and the higher pressure of the turbine inlet air
and the compressor outlet air upstream of the seal means 220 and 230,
respectively.
Advantageously, each of the first seal means 220 and second seal means 230
comprises a set of knife edge elements 222 and 232, respectively,
extending radially outwardly from and circumferentially about the
cylindrical central shaft sleeve 20c and a seal land 224 and 234,
respectively, mounted to and extending circumferentially about the inward
rim surface 14c of the annular disk-like member 14 in sealing
relationship with the knife like edge elements 222 and 232, respectively,
to form a labyrinth-like seal. The vent means 210 may comprise a plurality
of holes 207 disposed at circumferentially spaced intervals about and
extending through the central shaft sleeve 14c to open to a low pressure
interior region 21 defined within the hollow shaft means 20, as
illustrated in FIGS. 3 and 4. Alternatively, the vent means 205 could
comprise a plurality of holes provided in the stationary annular disk-like
member 14 and opening therethrough to an external low pressure region.
In either case, during operation of the air cycle machine 10 a limited
small amount of compressor outlet air flow passes from the compressor
outlet duct 164 through the annular opening 63 into the first volume 61
formed between the backside of the compressor rotor 60 and the root
portion 14a of the annular disc-like member 14 and thence leaks past the
knife edge seal means 230 and through the holes 207 forming the vent means
205 into the interior 21 of the hollow shaft means 20. At the same time, a
limited small amount of turbine inlet air flow passes from the turbine
inlet duct 152 through the opening 53 into the second volume 51 formed
between the backside of the turbine rotor 50 and the root portion 14a of
the annular disk-like member 14 and thence leaks past the knife edge seal
means 222 and through the holes 207 forming the vent means 210 into the
interior 21 of the hollow shaft means 20. Therein, the vented air flows
mix with the bearing air flow passing through the interior of the shaft
means and passes through the second journal bearing 80 before exiting
through seal 48 into the fan inlet duct 142.
Thus, the compressor air flow leaking past the knife edge seal means 230
will be desireably vented through the vent means 210 to a low pressure
region, which in the illustrated embodiment is the interior of the shaft
means 20, rather than passing into the turbine inlet duct 152, thereby
avoiding mixing of the warmer compressor outlet air flow with the cooler
air flow passing into the turbine. Additionally, by suitably sizing the
holes 207 forming the vent means 210, the annular volume 205 between the
spaced seal means 220 and 230 and upstream of the vent means 210 may be
maintained at a pressure between that of the compressor outlet air flow
and that of the relatively low pressure region within the hollow shaft
means 20. By careful selection of the vent hole size for a particular
design condition, the pressure within the annular volume 205 may be made
equal or about equal to the turbine backface pressure, i.e. the pressure
within the second volume 51, thereby ensuring that leakage of turbine
inlet air flow through the venting circuit will be desireably minimized.
As disclosed in commonly assigned co-pending application Ser. No.
07/819412, filed of even date, the annular disk-like member 14 may
advantageously comprise a relatively poor heat conducting member whereby
heat transfer across the annular disk-like member 14 from the relatively
warmer fluid passing into and out of the compressor rotor 60 to the
relatively cooler fluid passing into and out of the turbine rotor 50 is
retarded. By relatively poor heat conducting member it is meant that the
annular disk-like member 14 has a thermal conductivity which is at least
about an order of magnitude lower than the thermal conductivity of
conventional metals, typically aluminum, from which aircraft air cycle
machine components are made. Additionally, to reduce heat transfer from
the compressor rotor per se to the turbine rotor per se through the
central shaft sleeve 20c to which both the compressor and turbine rotors
are mounted, the central shaft sleeve 20c may comprise a relatively thin
walled, elongated sleeve made of a structural steel alloy having a thermal
conductivity lower than the thermal conductivity of the material from
which the rotors are made, which is typically aluminum. In the depicted
embodiment of the air cycle machine 10, the pressure differential imposed
across the radially outward portion 14b of annular disk-like member 14 is
advantageously minimized since the pressure of the air flow in the turbine
inlet duct 152 is only slightly less than the pressure of the air flow in
the compressor outlet duct 164, typically by only a few psi due to
pressure losses experienced as the air flow traverses the flow conduits
(not shown) from the compressor outlet duct 164 to the turbine inlet duct
152 and an intermediate heat exchanger (not shown) disposed therebetween.
The pressure differential across the radially inward root portion 14a of
the annular disk-like member 14 separating the back-to-back rotors 50 and
60 is also minimized as the compressor backside pressure in the first
volume 61 and the compressor backside pressure in the second volume 51 are
also relatively equal.
As the pressure differential across the annular disk-like member 14 is
maintained relatively low over its entire extent via the aforementioned
construction, the annular disk-like member 14 may be made from a
relatively low strength, low thermal conductivity, insulating material,
such as a non-metallic composite or ceramic material. Thus, the annular
disk-like member 14 may advantageously be formed of a fiber reinforced,
thermosetting resin material, such as an epoxy, polyimide or like resin
matrix reinforced with fiberglass, graphite, aramid or like fibers, with
the resin selected to give the desired low thermal conductivity and the
fiber selected to give the required strength. For example, the annular
disk-like member 14 may comprise a body of a polyimide resin matrix, such
as HyComp-M310 resin from Dexter Composites, reinforced with graphite
fibers to improve strength.
Although the invention has been shown and described with respect to a best
mode embodiment thereof, it should be understood by those skilled in the
art that the foregoing and various other changes, omissions, and additions
in the form and detail thereof may be made therein without departing from
the spirit and scope of the invention.
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